Elimination of key shocks



Aug. 8, 1933. H. RODER ELIMINATION OF KEY SHOCKS Filed Sept. 9, 1950INVENTOR HANS RODE R BY ATTORNEY Patented Aug. 8, 1933 UNITED STATESPATENT FFICE ELIMINATION OF KEY SHOCKS Hans Roder, Scotia, N. Y.,assignor to Tele funken Gesellsohaft fur Drahtlose Telegraphic m. b.H.,-Berlin, Germany, a Corporation of Germany Application September 9,1930, Serial No. 480,714, and in Germany September 17, 1929 10 Claims.

means for eliminating key shocks which areproduced principally by thekey operation of the plate circuit in transmitter tubes.

It-is known that when a receiver is mounted in the vicinity of atransmitter reception will be more or less seriously disturbed by thetransmitter for each key signal in the latter, or each rise and fall ofthe signal will be audible in the ;receiver set in the form of acracking noise Whichhas come to be known as key shocks. When thetransmitter {and the receiver equipments are installed in one and thesame room, and if furthermore the sending and the receiving antennae aremounted at relatively great proximity to each other, or even underneatheach other, then reception will become practically impossible so long asthe transmitter operates.

An attempt to obviate such key shocks by the provision of radiofrequency stoppers in the receiver set is practically hopeless inasmuchas the rapid start of the oscillation phenomenon contains a practicallycontinuous frequency spece trum. Hence, it is necessary to evolve waysand means for the transmitter which are adapted to limit this frequencyspectrum. This result is attainable by so regulating the rise and fallof the key signals that the .signals are'rounded. V

The present invention has as its principal aim and object that ofdisclosing a method with this end in view which will be useful inconnec-' tion with transmitter tube outfits which are imodulated by theinterruption of the plate direct current lead.

The invention has been illustrated in several of its preferred forms bythe accompanying drawing wherein:

Fig. 1 illustrates a self-excited tube set;

Fig. 2 illustrates a connection of resistors in the self-excitedtransmitter set; and,

Fig. 3 illustrates a modification of-Fig. 2 using the generator of Fig.2 as a pilot for another generator tube which is connected with thetransmitting antenna.

If in a self-excited transmitter set, as shown, for instance, by Fig. 1,the plate potential is broken, it is found that the ratio between platedirect current potential and plate direct current remains practicallyconstant until the oscillations eventually break oil when voltage Eassumes very low values. Hence, the generator tube could be conceived asbeing replaced by transmitter sharp edges of the.

the constant resistance RX. What logically follows from thisconsideration is this: when the current J is interrupted by the agencyof the key T the condenser C which has been charged up to potential Ewill be discharged by way of the resistance RX. Hence, amplitude of theradio frequency oscillation falls oil in direct proportion to voltage Euntil it finally breaks off suddenly as soon as E has attained a certainlow value. Now, this interruption would conceivably be audible in thereceiver apparatus in the form of a key shock; but the fact is that inpractice this stopping of the oscillation is free from any disturbingeffect inasmuch as it happens in the presence of a very small radiofrequency amplitude. But when closing or depressing the key T, thecapacity C is charged up almost instantaneously, in other words, theoscillations are started with great precision. For the above purpose,the arrangement is unserviceable inasmuch as the rise is too hard, andthe drop is too soft, considering the fact that Ex is a very highresistance.

The circuit scheme shown in Fig.2 illustrates one suitable system tocarry out the aim and object of this invention. When closing the key Tof the system shown by Fig. 2 a retarded charging up of the condenser Cby way of resistance R takes place, or, in other words, the initiationof the oscillations is smooth. When opening or releasing the key,resistance R is cut in the circuit and the capacity C is discharged bywayof the resistances 'R'+Rx so that the discharge proceeds at a muchfaster rate than previously. The softness or smoothness with which thesignals set in can be governed by the convenient selection of the valueof resistances R and R and the capacity C.

In parallel connection to resistance R in the key circuit is a chokecoil L adapted to avoid the fall 'of potential which otherwise wouldpermanently occur across the terminals of the resistor R, withoutprecluding the retarding influence of resistor B when closing thecircuit. The choke L is so dimensioned that the system comprising R, L,C and BK will'remain aperiodic.

The above keying scheme, of course, could just as readily be connectedin the plate lead of a separately or pilot exicted transmitter or elsebe included in the input stages of a separately-excited transmitter.

Using the generator tube connected in a Way as shown in Fig. 2 as apilot generator for another "generator tube as shown in Fig. 3, then anysudden change in the antenna current is avoidable by imparting andapplying to the grid of the output stage a negative grid biasingpotential Ev. To be sure, the pilot tube breaks off suddenly andabruptly whenever the values of E and therefore also of Eg and Ev arelow; but it can be so adjusted that the antenna curr nt will alreadyhave died down to zero value when the sudden change of Eg occurs.

Other modifications and changes may suggest themselves to those skilledin the art to which the invention relates, and I, therefore, believemyself to be entitled to make and use any and all or" such modificationsas fairly fall within the spirit and scope of the hereinafter appendedclaims.

Having now described my invention, what. I claim and desire to secure byLetters Patent'is the following:

1. In combination with a keying system for avoiding key shocks intransmitter tubes wherein when the plate supply lead to the transmittertube is opened bykeying the signal amplitude decreases and increaseswhen the lead is closed keying, a resistor in series with the key whenthe lead is closed for retarding the rise of keyin impulses, a chokecoil connected iii-parallel with said resistor for avoiding the drop inpotential across the said resistor, a second resistor in series withsaid key when the plate supply lead is opened by keying for acceleratingthe decrease in keying impulses during periods when the key is opened,means for connecting the generator tube with a'second transmitting tube;

and means for applying a negative biasing poand inductively con 'cuitsconnected betvwen said electrodes comtential to the transmitting tubeor" such value repeater having input and output electrodes and separatedinput and output circuits connected with said electrodes comprising, asource of direct current potential having one terminal connecteddirectly to an output electrode, a key connected to the other outputelectrode, a contact associated with said key, a resistance andinductance connected in parallel between said contact and the otherterminal of said source,

and a capacity connected in parallel with the impedance between theoutput electrodes of said tube.

3. Keying means for a thermionic relay tube having input and outputelectrodes and separated input and output circuits connected with saidelectrodes comprising, a source of direct current potential havingoneterminal connected to an output electrode, a switch connectedto theother output electrode, a contact associated with said switch, aresistance and inductance connected in parall l between said contact andthe other electrode oi aid source, and a second resistance havoneterminal connected to one of said output electrodes and the otherterminal connected with; a contact adjacent said switch whereby saidresistance may be connected in parallel with the output electrodes ofsaid tube;

4. Keying means a thermionic oscillation generator having in ut andoutput electrodes d input and output cirisiiig, aisource of directcurrent potential havsaid output electrodes, a capacity connects inparallel with the impedance between said output electrodes, a switchconnected with one terg one'terminal connected directly to one of minalof said capacity, a pair of contacts, and means for retarding the risein the potential applied to said output electrode and the charging rateoi said condenser connected in parallel with the impedance between theoutput electrodes of said tube including, an inductance and a resistancein parallel connected between one of said contacts and the otherterminal or" said source, and means for increasing thedisclrargingrateof said capacity comprising a resistance connectedbetween the other of said contacts and the other terminal of saidsource.

5. Keying means to be used with thermionic repeaters having input andoutput electrodes and input and output circuits connected between saidelectrodes comprising, a source of direct current potential having oneterminal connected to one of said output electrodes, a capacityconnected in parallel with the impedance between said output electrodes,a switch connected with one terminal of said capacity, a pair ofcontacts, and means for retarding the rise in the potential applied tosaid output electrode and in the charging rate of said condenserconnected in parallel with the impedance between the output electrodesof said tube including, an inductance'and a resistance in parallelconnected between one of said contacts and the other terminal of saidsource, and means for increasing the discharging rate of said capacitycomprising a resistance connected between the other of said contacts andthe other terminal of said source.

6. Keying means for a thermionic oscillation generator having input andoutput electrodes and inductively coupled input and output circuitsconnected between said electrodes comprising, a source of direct currentpotential having one terminal connected to one of said outputelectrodes, a capacity connected in parallel with the impedance betweensaid output electrodes, a switch connected with one terminal of saidcapacity, a pair of contacts, and means for retarding'the rise in thepotential applied to said output electrode, and the charging rate ofsaid con denser connected in parallel with the'impedance between the.output electrodes of said tube including, an inductance and- 'aresistance in parallel connected between one of said contacts and theother terminal of said source, means for increasing the discharging rateof said capacity comprising a resistance connected between the other orsaid contacts and the other terminal or" said source, and a thermionicrepeater having its input circuit associated with the output circuit ofsaid generator.

7. Transmitting means comprising, a thermionic oscillation generator;having its anode, cathode and control grid electrodes connected inoscillation circuits, means for interrupting said oscillations at signalfrequency comprising a key having a signalling position and a spacing ornon-signalling position, a source of direct current potential having oneterminal connected to the cathode of saidoscillation generator, a firstcontact connected to the other terminal ofsaid source,'a connectionbetween said key and the anode of said generator, means for preventingan abrupt increase in direct current potential on said anode when saidkey is in the, signalling position on said first contact comprising, aresistance connected between said first contact and said source, andmeans for insuring a rapid falling off of the oscillations generatedwhen said key is in said spacing or non-signalling position comprising,a second resistance havingone terwhich a charging capacity is connectedin parr allel with the anode to cathode impedance of said tube in eitherposition of said key.

10. An arrangement as claimed in claim 7 in which an inductance isconnected in parallel vwith said first named resistance and in which acharging condenser is connected in parallel with said second namedresistance when said key is in the spacing or non-signalling position.

HANS RODER.

